1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display device, and more particularly, to an OLED display device having high aperture ratio and high resolution and a method of fabricating the same with low production costs.
2. Discussion of the Related Art
As the society has entered in earnest upon an information age, a field of display devices that represent all sorts of electrical signals as visual images has developed rapidly. Particularly, the liquid crystal display (LCD) device or the OELD device as a flat panel display device having characteristics of light weight, thinness and low power consumption is developed.
The LCD device uses optical anisotropy and polarization properties of liquid crystal molecules. The LCD device is adequate to display moving images and has high contrast ratio.
The LCD devices require a liquid crystal panel including first and second substrates and a liquid crystal layer interposed therebetween. An arrangement of the liquid crystal molecules in the liquid crystal layer is changed by an electric field induced in the liquid crystal panel to control light transmissivity.
Generally, an additional light source is required because the liquid crystal panel is a non-emissive-type display device. Accordingly, a backlight unit is disposed under the liquid crystal panel. The LCD device displays images using light produced by the backlight unit and supplied to the liquid crystal panel.
On the other hand, the OLED display device is a self-emission type display device such that the backlight unit as a light source is not required. As a result, there are advantages in the fabricating process and thinness in the OLED display device.
In addition, the OLED display device has advantages in a viewing angle, a contrast ratio, a response time, power consumption in comparison to the LCD device. Moreover, since the elements of the OLED display device are solid, the OLED display device has high impact-resistance. The OLED display device for a high resolution and a large size is widely researched.
FIG. 1 is a plane view of the related art OLED display device.
As shown in FIG. 1, on a substrate 1a of the OLED display device 1, a plurality of power lines 51, a plurality of data lines 53 and a plurality of reference voltage lines 55 are formed. At an edge of the substrate 1a, a plurality of pads 70, which are connected to the power lines 51, the data lines 53 and the reference voltage lines 55 through link lines 61, are formed.
A drive integrated circuit (IC) are installed at the edge of the substrate 1a, and first and second chip on films (COFs) 10a and 10b, each of which includes a plurality of pads 11, are connected to the drive IC. Each of the plurality of pads 70 formed at an upper edge of the substrate 1a is connected to each of the plurality of pads 11 formed at the first and second COFs 10a and 10b. The connection between the pads 70 and the pads 11 is conducted by a conductive adhesive such as an activated carbon fiber (ACF) including conductive balls.
The first and second COFs 10a and 10b are attached to a lower edge of the substrate 1a. The first and second COFs 10a and 10b at the lower edge overlap the first and second COFs 10a and 10b at the upper edge by 180 degree rotation.
As shown in FIG. 1, one power line 51, two data lines 53, one reference voltage line 55 and two data lines 53 are arranged from a side, i.e., a left side, of the substrate 1a as a line group. In addition, another one power line 51 is arranged at an end of a right side.
With the above line arrangement, a first dummy pad 11a is formed at an end of the right side of each of the COFs 10a and 10b. In addition, a second dummy pad 70a is formed at the substrate 1a to correspond to the first dummy pad 11a. Namely, the line arrangement is asymmetric such that the first and second dummy pads 11a and 70a are not connected to the power line 51. In addition, a design of a driving printed circuit board, which is connected to the COFs 10a and 10b, becomes difficult because of the first dummy pad 11a in the COF 10a. 
The OLED display device is fabricated by a mask process for forming thin films by patterning a material layer. The mask process includes a step of forming a photoresist layer, a step of exposing the photoresist layer using an exposing mask, a step of developing the exposed photoresist layer to form a photoresist pattern, a step of etching the material layer using the photoresist pattern as an etching mask, and a step of removing the photoresist pattern.
In the large size substrate 1a, a stitching exposure is performed with respect to a boundary between the first and second COFs 10a and 10b. However, when the large size OLED display device is fabricated by the stitching exposure, there is a stain problem, i.e., a stitch defect, at the boundary between the first and second COFs 10a and 10b. 